Nicotine and ethanol are the two most co-abused drugs in the world and it is estimated that 50-90% of alcoholics smoke cigarettes suggesting a functional interaction exists between nicotine, the primary addictive component of tobacco smoke, and ethanol, in dopaminergic brain areas involved in addiction. Neuronal nicotinic acetylcholine receptors (nAChRs), the molecular targets of nicotine, have been implicated in the reinforcing properties of ethanol, but, despite this association, the specific nAChR subtypes mediating these effects are unknown. The goal of this proposal is to utilize a combination of nicotinic receptor mouse models, pharmacology, behavioral assays, and electrophysiology to test the hypothesis that 4* nAChRs, previously found to be paramount in initiating nicotine dependence, are also involved in the physiological and behavioral response to ethanol, and the cross-dependent properties of nicotine and ethanol. Mouse models that either do not express high affinity 4* nAChRs, or that express hypersensitive 4* nicotinic receptors 50-fold more sensitive to agonist, will be utilized to test the hypothesis that activation of these receptors is critical for ethanol consumption, preference, and reward. In addition, we will test the hypothesis that 4* nAChRs are necessary for nicotine-ethanol cross-tolerance as it pertains to alcohol self-administration by measuring ethanol consumption, preference, and reward after chronic nicotine treatment in these mouse lines. In aim 3, we will use a biophysical approach to test the hypothesis that ethanol modulation of nicotinic responses and excitability of dopaminergic VTA midbrain neurons is dependent on 4* nAChR expression and activation. It is anticipated that the results from these experiments will yield valuable insight into the biology of alcohol dependence, as well as identify potential targets for alcohol cessation therapeutics.